Chain caesium borophosphates with B:P ratio 1:2: synthesis, structure relationships and low-temperature thermodynamic properties

Abstract

Three caesium‐bearing borophosphates, Cs[BP2O6(OH)2] (I), Cs0.51Mn1.17(H2O)2[BP2O8]·0.45H2O (II) and CsMn[BP2O8(OH)] (III), were synthesized by a hydrothermal method at 473–523 K. Their crystal structures have been studied by means of single‐crystal X‐ray diffraction; all three structures comprise borophosphate chain anions with a B:P ratio of 1:2. The unique construction of (I) is based on four‐membered‐ring chains running parallel to the [010] direction. These protonated borophosphate chains are linked via hydrogen‐bond interactions to form a 3D framework with caesium cations incorporated. (II) is the first Cs and Mn2+,Mn3+ member of a known family characterized by [BP2O8]∞ helical chains running along [001]. These chains are connected through MnO4(H2O)2 octahedra to form a 3D framework. The caesium cations are disordered over two independent positions in the channels, which they occupy together with water molecules. An additional MnO2(H2O)3 bipyramid statistically shares a common edge and two corners with three main Mn octahedra to form tetrameric clusters. The topological relation between the chain anionic fragments of (I) and (II) as well as the structural relation between (I) and previously studied boro‐ and berillophosphates are discussed. Compound (III) presents the first Mn member of the AIMIII[BP2O8(OH)] family and is characterized by a 3D framework built by open‐branched borophosphate chains and MnO5 semi‐octahedra sharing vertices. The measurements of thermodynamic properties, i.e. magnetization M and specific heat Cp, to 2 K and 30 T, provide evidence that (II) orders antiferromagnetically at the Néel temperature TN = 4.6 K and exhibits a plateau‐like feature under the action of an external magnetic field accompanied by a pronounced magnetocaloric effect.

Polytypism of Compounds with the General Formula Cs{Al2[TP6O20]} (T = B, Al): OD (Order-Disorder) Description, Topological Features, and DFT-Calculations

“…As a reference structure for the further analysis, the MDO1 polytype observed in Cs{Al 2 [AlP 6 O 20 ]} [26] was used. This compound was reported in the nonstandard setting of the space group C2cb [a = 10.0048 (7) Å, b = 13.3008 (10) Å, c = 12.1698 (7) Å], which was transformed into the standard setting Aea2 using the [00-1/010/100] matrix (the resulting unit cell parameters are: a = 12.1698(7) Å b = 13.3008 (10) Å, c = 10.0048(7) Å). The unit-cell parameters and space groups of the crystal structures of Cs{Al 2 [BP 6 O 20 ]} polytypes have been transformed accordingly in order to preserve the orientation and stacking direction of the OD-layers.…”

“…Borophosphates (as well as borophosphate ceramics and glasses) attract interest because of their wide technological applications as materials with optical [1][2][3][4][5], electrochemical [6][7][8][9], magnetic [10][11][12], and catalytic [13][14][15] properties. Moreover, crystalline borophosphates and metal borophosphates with microporous structures are considered as zeolite-like materials [16][17][18][19][20].…”

K2Mn3O(OH)(VO4)(V2O7) with Sawtooth Chains of Multivalent Manganese Triangular Trimer Units: Magnetic Susceptibility Shrouding a Long-Range Antiferromagnetic Order of Ferromagnetic Triangles

“…They include the oxide� hausmannite, Mn 2+ ders antiferromagnetically and exhibits a plateau-like feature in the magnetic field and a pronounced magnetocaloric effect. 3 To date, there has been no report on ortho-pyrovanadates consisting of both Mn 2+ and Mn 3+ (d 4 ) ions.…”

“…Synthetic mixed-valent manganese compounds, recently reported, include phosphates, K 3 Mn 3 2+ Mn 3+ (PO 4 )­(H 0.5 PO 4 ) 2 (HPO) 2 and PbMn 2 2+ Mn 3+ (PO 4 ) 3 , as well as the borophosphate, Cs 0.51 Mn 0.17 3+ Mn 2+ (H 2 O) 2 [BP 2 O 8 ]·0.45H 2 O. The latter orders antiferromagnetically and exhibits a plateau-like feature in the magnetic field and a pronounced magnetocaloric effect . To date, there has been no report on ortho -pyrovanadates consisting of both Mn 2+ and Mn 3+ (d 4 ) ions.…”